The electrical signals responsible for neuronal communication and cardiac rhythmicity depend on potassium channels, proteins that regulate the movement of potassium ions across cell membranes. The disruption of these channels by inherited diseases or drugs can lead to neurological defects or cardiac arrhythmias.

Work in our lab focuses on voltage-gated potassium channels encoded by the
human Ether-a-go-go-Related Gene, or hERG1. In 1995, we showed that hERG1 expressed in Xenopus oocytes produces
currents with the unique biophysical and pharmacological properties of the cardiac repolarizing current known as IKr.
This work established hERG1 channels as a potential target for acquired long QT syndrome (LQTS), in which block of IKr by drugs intended
for a wide range of therapeutic targets can trigger life-threatening ventricular arrhythmias known as torsades de pointes.
In addition, these studies explained the underlying cause of inherited type 2 LQTS (LQT2), which had been linked to the hERG1 gene,
as a loss or reduction of cardiac IKr

In subsequent studies we have shown that the hERG gene encodes two closely related subunits that readily assemble
to form IKr in native tissues. hERG 1a, the original hERG isolate, and hERG 1b are identical except for their cytoplasmic,
amino (N) termini, which are non-homologous domains that interact in the earliest stages of biogenesis to promote subunit oligomerization.
hERG 1b subunits expressed alone fail to produce robust currents because of an exposed endoplasmic reticulum (ER) retention signal that
is masked by association with 1a. hERG 1a/1b heteromers produce more current than hERG 1a homomeric channels because they open
more quickly and because they spend less time in the inactivated state at positive potentials.
These differences in gating kinetics can all be attributed to the reduced number of 1a N termini, which modulate channel gating properties.
These studies illustrate the importance of the 1b subunit in the oligomeric complex that produces IKr, and establish hERG 1b-specific
sequences as potential targets for LQT2.

In this post-genomic era, we are close to knowing the composition and stoichiometry of all ion channels in the heart and other excitable tissues. Yet we know little about the mechanisms that regulate surface expression and relative numbers of different channel types. In the heart, even a minor perturbation of this delicate balance can have catastrophic consequences. Our efforts are currently focused on determining mechanisms of surface expression, understanding the checkpoints of hERG trafficking (each of which represents a potential LQTS target), and therapeutic approaches that can restore normal physiological function to a diseased heart.

Another area of investigation in the lab is acquired LQTS, which affects an estimated 1-8% of the general public.
We now know that most compounds that cause this adverse drug reaction are hERG blockers, so early screening for hERG block in the drug
discovery process is used to ensure these compounds do not reach the pharmacy shelves. However, a staggering 70% of lead compounds block hERG,
so most compounds are dropped from development before their efficacy for therapeutic applications can be realized.
We are studying why drugs block hERG but not structurally related channels. We are interested in genetic variations and disease states that reduce
the numbers of functional hERG channels to subclinical levels until additional stressors such as hERG-blocking drugs further diminish repolarization
and trigger torsades de pointes arrhythmias. One long-range goal of this work is to develop a genetic screen that protects susceptible
individuals from harm while removing the barriers that currently impede the development of life-saving therapeutic treatment options
in the broader population. Another is to develop therapeutics that promote hERG channel expression and counteract the adverse
effects of other drugs and disease states on cardiac repolarization.

We employ a wide array of techniques to address these objectives.
We use electrophysiological techniques such as voltage clamp and patch clamp from Xenopus oocytes and HEK-293 cells to monitor gating
kinetics and surface channel expression levels. We carry out biophysical analysis of gating in normal and mutant channels together
with molecular modeling to identify structural domains of channel function. We also use protein biochemistry to monitor oligomeric
assembly of channel subunits, subcellular hERG trafficking and interactions of hERG with proteins in the trafficking pathway.
We complement these cellular studies with confocal immunocytochemistry.

Current Lab Members

Phu Tran, Ph.D.

Postdoctoral Fellow

Sunita Joshi

Graduate Student - Cell and Molecular Biology

Yaxian Zhao

Graduate Student - Physiology Graduate Training Program

Abdalla Saad

Senior Research Specialist

Fang Liu

Research Specialist

Past Lab Members

Matthew Trudeau, Ph.D.

Assistant Professor, Univ. of Maryland School of Medicine

Ian Herzberg, Ph.D.

Regional Sales Manager, Brookhaven Instruments

Janet Branchaw, Ph.D.

Undergraduate Education Coordinator for the Center for Biology Education, UW-Madison